This paper presents a nonlinear numerical analysis on the seismic behavior of concrete filled square steel tube (CFST) columns and steel beam planar frame with through bolt-endplate beam-column connection, by using the finite element analysis modeling with ABAQUS. Parametric studies were conducted to investigate the influence of axial load ratio and beam-to-column linear stiffness ratio on the seismic behavior of composite frames. The analysis results were in good agreement with the experiment results. The analysis results showed that CFST frame with through bolt-endplate beam-column connection had good seismic behavior. The increase of axial load ratio will degrade the horizontal load bearing capacity and increase the energy dissipation capability. The increase of beam-to-column linear stiffness ratio will increase the horizontal load bearing capacity and degrade the energy dissipation capability.